10-Year Study Shows Electron Is Surprisingly Spherical

Photonics.comMay 2011
LONDON, May 26, 2011 — Using a very precise laser, physicists have made the most accurate measurement of the shape of an electron, deeming it 0.000000000000000000000000001 cm from being perfectly round. This means that if the electron were magnified to the size of the solar system, it would still appear spherical to within the width of a human hair.

Physicists from Imperial College London's Centre for Cold Matter studied the electrons inside molecules called ytterbium fluoride. Using a very precise laser, they made careful measurements of the motion of these electrons. If the electrons had not been perfectly round, their motion would have exhibited a distinctive wobble, as with an unbalanced spinning top, distorting the overall shape of the molecule. The researchers saw no sign of such a wobble.

The researchers are planning to measure the electron's shape even more closely. The results of this work are important in the study of antimatter, an elusive substance that behaves in the same way as ordinary matter, except that it has an opposite electrical charge. For example, the antimatter version of the negatively charged electron is the positively charged anti-electron (also known as a positron). Understanding the shape of the electron could help researchers understand how positrons behave and how antimatter and matter might differ.

New research suggests the electron is surprisingly spherical — much more spherical than, say, a common billiard ball. (Image: Hedgehog / Fotolia)
“We're really pleased that we've been able to improve our knowledge of one of the basic building blocks of matter. It's been a very difficult measurement to make, but this knowledge will let us improve our theories of fundamental physics,” said Dr. Jony Hudson, researcher from the department of physics at Imperial College London. “People are often surprised to hear that our theories of physics aren't 'finished,' but in truth they get constantly refined and improved by making ever more accurate measurements like this one.”

The currently accepted laws of physics say that the Big Bang created as much antimatter as ordinary matter. However, since antimatter was first envisaged by Nobel Prize-winning scientist Paul Dirac in 1928, it has been found only in minute amounts from sources such as cosmic rays and some radioactive substances.

Imperial's Centre for Cold Matter aims to explain this lack of antimatter by searching for tiny differences between the behavior of matter and antimatter that no one has yet observed. Had the researchers found that electrons are not round, they would have found proof that the behavior of antimatter and matter differ more than physicists previously had thought. This, they say, could explain how all the antimatter disappeared from the universe, leaving only ordinary matter.

“The whole world is made almost entirely of normal matter, with only tiny traces of antimatter,” said Edward Hinds, professor and head of the Centre for Cold Matter. “Astronomers have looked right to the edge of the visible universe and even then they see just matter, no great stashes of antimatter. Physicists just do not know what happened to all the antimatter, but this research can help us to confirm or rule out some of the possible explanations.”

Antimatter is also studied in tiny quantities in the Large Hadron Collider at CERN in Switzerland, where physicists hope to understand what happened in the moments following the Big Bang and to confirm some currently unproven fundamental theories of physics, such as super symmetry. Knowing whether electrons are round or egg-shape tests these same fundamental theories, as well as other theories of particle physics that even the Large Hadron Collider cannot test.

To help improve their measurements of the electron's shape, the researchers now are developing new methods to cool their molecules to extremely low temperatures, and to control the exact motion of the molecules. This will allow them to study the behavior of the embedded electrons in far greater detail than ever before. They say the same technology could also be used to control chemical reactions and to understand the behavior of systems that are too complex to simulate with a computer.